Well in that case Im at a loss, sorry I couldn't be more helpful.
Only other thing I can think of that might be causing this is the codes having bad pointers (that'd explain why max items gives you a monster instead) but I don't know how to fix that.
ya, we're on identical setups. Just to be 100% sure it's not an issue with filezilla would you mind taking out your sd card and moving the plugin manually?
Just tested your plugin, everything seems to work in smt4, you're definitely playing smt4:A.
Next time check your title keys, afaik the cheat menu should always pop up if you have it assigned to the right game even if none of the codes are working.
If you just want to use premade cheats you can use NTRCCompiler to make a plugin instead. https://gbatemp.net/threads/release-ntrccompiler-2-0.462445/
Nanquitas' program has a tendency to crash my 3ds and has pretty limited use (at least until it gets an update that makes the pointer scan...